The present invention relates to an implantable electrode lead and, more particularly, to a technique for forming a predetermined portion of the lead body of an atrial lead into a desired shape such as a xe2x80x9cJxe2x80x9d shape in order to use the implantable electrode lead together with, e.g., a heart pacemaker or implantable defibrillator.
Many conventional implantable electrode leads used together with heart pacemakers and implantable defibrillators are known. An implantable electrode lead is generally comprised of at least one electrode for supplying an electrical stimulation pulse or sensing an electrical evoked response of the heart, an electrical connector for connecting the electrode lead to a heart pacemaker or implantable defibrillator, and a lead body inserted between the electrode and the electrical connector and made up of a biocompatible insulating sheath and a conductor coil for transmitting an electrical signal between the electrode and the heart pacemaker or implantable defibrillator.
In an electrode lead for cervical vein, the distal-end electrode is indwelled in the heart via the vein, and the proximal-end electrode is connected to the connection housing of the heart pacemaker or implantable defibrillator. The implantable electrode leads are classified into atrial and ventricular leads. The ventricular lead electrode is generally indwelled in the apex of the right ventricle, while the atrial lead electrode is generally indwelled in the right atrial auricle. The atrial lead has a J-shaped portion near its distal end to facilitate indwelling of the electrode in the auricle. A general means for imparting the J shape to the atrial lead is comprised of an insulating sheath or conductor coil serving as a constituent element of the lead body. As a means for imparting the J shape to the atrial lead, a separate reinforcing member is disposed to impart the J shape or to hold the J shape in one or both of the insulating sheath and the conductor coil. The implantable electrode lead has a cavity for receiving a stylet. When the stylet reaches the J-shaped portion at the distal end of the atrial lead, the distal end of the atrial lead follows the shape of the distal end of the stylet. When the stylet is retracted to the proximal-end side, the distal end of the atrial lead restores the J shape. The atrial lead electrode is indwelled in the atrial auricle using such stylet movement.
Imparting a desired shape to the implantable electrode lead is not limited to the J shape of the atrial lead. Japanese Patent Laid-Open No. 5-49701 to Nakajima discloses a technique for forming a special shape such as a desired helical shape in the lead body.
As one of the state-of-the-art means for imparting the J shape to an atrial lead, the J shape is imparted to a constituent element of a lead body. To increase the rigidity of the insulating sheath or conductor coil, however, the outer diameter of the lead body increases, and flexibility of the whole lead body degrades. An increase in outer diameter of the lead body may cause hemostasis. The lack of flexibility of the lead body increases the mechanical stress inflicted on a living body by the lead body.
It is difficult to obtain a sufficient retaining force for maintaining the J shape in a thin flexible silicone atrial lead. It is therefore considerably difficult to indwell the electrode in the atrial auricle. According to the conventional method of imparting the J shape to a constituent element of a lead body, when a lead structure described in Japanese Patent Laid-Open No. 11-333000 proposed to improve the durability of the lead body is applied to an atrial lead, it is difficult to obtain a sufficient retaining force for maintaining the J shape.
For example, U.S. Pat. No. 4,454,888 discloses a case in which a metal wire is used as a separate reinforcing means to reinforce the J shape. According to this disclosure, when the metal wire breaks, the metal wire bores into the insulating sheath to the outside, thus posing problems as to safety and reliability.
The present invention has been made in consideration of the conventional problems described above, and has as its object to provide an implantable electrode lead which can have a small diameter with flexibility and can maintain a desired portion of a lead body to a desired shape conforming to a predetermined portion of a living body.
In order to solve the conventional problems described above and achieve the above object, according to the present invention, an implantable electrode lead having a lead body for performing at least one of transmission of an electrical stimulation pulse generated by an implantable device to a living body and transmission of an electrical signal from the living body to the implantable device, the lead body having at least one electrode at a distal end thereof, and connector for mechanically and electrically connecting a proximal position of the lead body to the implantable device, characterized in that the lead body comprises a conductor coil obtained by helically winding at least one insulation-coated electrical conduction conductor wire and an insulating sheath made of an electrically insulating resin material to cover an outer surface of the conductor coil, and a flexible reinforcing tube shaped to deform into a desired shape is disposed in a cavity of the conductor coil, thereby maintaining a predetermined portion of the lead body in the desired shape.
According to an aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the predetermined portion is located near a distal end of the lead body, and the desired shape is a substantially J shape.
According to another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the reinforcing tube is made of a predetermined resin material containing polyimide.
According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that rigidity of the reinforcing tube is higher than rigidity of a combination of the coil and the insulating sheath.
According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the reinforcing tube is formed into the desired shape beforehand prior to assembly.
According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that after the reinforcing tube is disposed in the cavity of the coil in a straight state, the reinforcing tube is shaped to obtain the desired shape.
According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the distal end of the reinforcing tube is connected to the electrode, and a proximal end of the reinforcing tube is connected to the connector.
According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the lead body has a size of not more than 2 mm, the insulating sheath is made of an electrically insulating, flexible resin material having a Shore hardness of less than 80 A, and the conductor coil has a spring index D/d (average diameter of coil/diameter of conductor wire) of more than 7.8.
According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the conductor coil comprises a multi-wire coil obtained by winding a plurality of insulation-coated conductor wires in the same average diameter.
According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the conductor wire comprises a multi-wire coil and the electrode is divided into a plurality of electrode portions such that one of wires of the multi-wire coil transmits one electrical signal and remaining ones of the multi-wire coil transmit remaining electrical signals.
According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that an insulation coating of the conductor coil is made of fluoroplastic.
According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the conductor wire has a composite or cladding structure of a first metal material having a low resistivity and a second metal material excellent in corrosion resistance and mechanical characteristics.
According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that a cavity for receiving a straight stylet is formed in the reinforcing tube, the stylet is inserted into the cavity to deform the desired shape of the predetermined portion of the lead body into a linear shape, and the desired shape is then restored by removing the stylet.
According to still another aspect of the implantable electrode lead of the present invention, the implantable electrode lead is characterized in that the implantable electrode lead is applicable to the implantable electrode lead described in Japanese Patent Laid-Open No. 11-333000, and a flexible reinforcing tube formed into a desired shape is disposed in the cavity of the coil to form the predetermined portion of the lead body in the desired shape.
With the above arrangements, a flexible, thin implantable electrode lead can provide reinforcing means for forming the predetermined portion of the lead body into a desired shape. Since the reinforcing means is comprised of a tube and disposed in the cavity of the coil, a danger of the reinforcing means boring into the insulating sheath to the outside can be prevented. In addition, when the reinforcing means is imparted with, e.g., the J shape of an atrial lead, the atrial lead can have better operability. Movement and removal of the electrode upon surgical operation can be prevented.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.